Prolactin mRNA has been purified by immunoprecipitation of polysomes, oligo (dT) cellulose chromatography and sucrose gradient centrifugation. This RNA was purified 320-fold and is greater than 95% pure as determined by cell-free translation. In addition recombinant DNA containing the coding sequence of rat preprolactin has been constructed and amplified in bacteria. Future work will involve the use of this cloned DNA to investigate prolactin mRNA metabolism. The kinetics of prolactin mRNA degradation will be determined. Also, the synthesis and processing of nuclear precursors of prolactin mRNA will be examined.